The latest research shows that all of us can pump up our brainpower by exercising regularly

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2: Aim for 150 minutes of moderate exercise a week

Do the math — that's just 2-1/2 hours a week. "To get the brain benefit of exercise, the gold standard is 150 minutes of aerobic exercise, such as walking briskly, spread over the course of a week," says Medina. (Be sure to warm up before and cool down after with gentle stretches for five minutes.)

Nor do you have to train for a marathon to reap brain benefits. In a recent Canadian study, researchers followed a large group of elderly adults for 2-5 years. None were fitness fanatics; their daily activities included walking, cooking, gardening and cleaning house. The results were stunning: Year after year, 90 percent of those who were consistently active showed no decline in their ability to think and remember.

Anything that gets your heart beating faster works. "You want to break a light sweat and feel like you're huffing and puffing,'' says Majid Fotuhi, M.D., medical director of the Neurology Institute for Brain Health and Fitness in Lutherville, Md., "but you should still be able to speak."

Does it still count if you break up those 150 minutes into lots of smaller spurts? "That's the million-dollar question," says Erickson. "These figures have been largely based on studies of cardiovascular disease. While it's true that what's good for the heart is good for the brain, we can't say for sure that the figures also apply to brain fitness."

Tips:

Go green. In a study from Ohio State University, people were more likely to stick with an exercise regimen when they were exercising outdoors. And researchers in Britain found that people who strolled through a park or other outdoor environment, as opposed to exercising indoors, had a measurable boost in focus, energy and well-being.

Sneak it in. Park your car at the far end of the mall lot. Get off the bus several stops before home, or walk up and down the field during your grandchild's soccer game.

If joints are stiff and muscles weak, try a low-impact workout like walking in the pool or taking a spin on a stationary bike. Pilates, yoga and tai-chi also place minimal stress on the body but still strengthen core muscles and improve balance. Never done any of that? All the better! As you'll read in our article on mental workouts, learning something new is another important pillar of brain health.